1. Field of the Invention
The present invention relates to a surface treating method of a granular material formed by polishing a rice, a barley, a Japanese millet, a foxtail millet, an adlay, or the other grains, or kneading and solidifying a starch such as a tapioca.
2. Description of the Prior Art
In the rice, the barley, the Japanese millet, the foxtail millet, the adlay, or the other grains, a xe2x80x9cbranxe2x80x9d or the like attached to a surface thereof or forming a part of the surface is removed by polishing prior to being served as a food. Further, a miscellaneous grain crop, a corm or the like is once formed into fine particles so as to be made a dry starch, and thereafter is kneaded and solidified, thereby being processed to a granular material having a fixed size such as the tapioca.
Since the polished grains or the processed granular materials mentioned above mainly contain a starch, an entrained component such as a fat and an oil or the like oozes out and an oxygen, a moisture or the like enters into an internal portion, whereby the polished grains or the processed granular materials change in quality. Accordingly, these materials are not proper to be kept or stored for a long time.
For example, with respect to the rice, there is performed a method of removing a bran component on the surface and an aleurone layer by polishing a brown rice so as to obtain a polished rice and further removing a skin bran by brushing it so as to obtain a milled rice.
Since the polished rice has less bran component and aleurone layer in comparison with the brown rice, the polished rice less changes in quality, so that the taste thereof is deteriorated at a lower degree during the storage within a given period.
However, on the contrary, since the polished rice is not covered with the bran component or the aleurone layer, the oil and fat easily oozes out to the surface at that degree and the oxygen, the moisture or the like easily enters into the internal portion, so that there is a problem the polished rice is easily oxidized and changes in quality, thereby being improper to be kept or stored for a long period.
An object of the present invention is to provide a treating method of forming a protection layer having strong abrasion resistance and oxidation resistance and having a thickness of micron order of a surface of a polished grain or a processed granular material so as to make it hard to be changed in quality, thereby improving a storage capacity for a long time.
Further, another object of the present invention is to provide a treating method of forming fine particulate starches attached to the grain or the granular material into a paste state so as to combine with the protection layer.
The prevent invention solves the problems mentioned above by means of applying a high humidity hot wind to a polished grain or a processed granular material so as to heat a surface layer portion, forming a starch in the heated portion into a paste state, making the starch into an alpha state, cooling the portion and forming a fine layer of the alpha starch.
The method in accordance with the present invention is to apply the high humidity hot wind to the granular material such as the polished grain or the like so as to form the starch in the portion between some microns and some hundreds microns of the surface of the granular material into a paste state due to the heat and the moisture, further to make the starch into an alpha state so as to form the alpha starch layer having a fine density and a high abrasion resistance, and to cool the alpha starch layer.
A temperature and a humidity (moisture containing amount) of the high humidity hot wind and a heating time of the granular material are determined on the basis of a quality of the raw material granular material and a thickness (between some microns and some hundreds microns) of the alpha starch layer required for the product granular material.
That is, when applying the high humidity hot wind to the granular material, the starch of the surface portion is at first formed into a paste state, and next it is made into an alpha state.
In this case, the fine-powder-shaped starch attached to the surface of the granular material is also simultaneously formed into a paste state so as to be attached to the granular material, thereby being integral with the granular material.
The raw material granular material has a tendency that the surface portion is easily formed into a paste state as the contained moisture becomes higher, and the paste state and the alpha state of the starch of the surface portion of the granular material can be securely promoted as the heating time becomes longer, whereby the thickness of the alpha starch layer is increased.
In this case, when the temperature of the high humidity hot wind is over a fixed temperature, for example, 250xc2x0 C., a speed at which the portion is dried becomes greater than a speed at which the starch is made into a paste state in accordance that the temperature becomes higher, whereby the alpha starch layer becomes thin.
Further, when the heating operation is continued after the alpha starch layer is generated, the alpha starch layer is dried, the density fineness is reduced to weaken the layer, and a crack is going to be generated on the surface of the granular material. In this case, when the heating operation is further continued, the heat is transmitted to an inner side of the alpha starch layer, the starch at this portion is made into an alpha state and the contained moisture is reduced, whereby the granular material becomes not xe2x80x9ca raw ricexe2x80x9d.
Accordingly, in view of this point, the high humidity hot wind is to be properly set such that a temperature is about 85 to 300xc2x0 C., a humidity is about 50% or more, and a heating time is about 1 to 10 seconds, and in the case that a temperature is about 200 to 300xc2x0 C., the heating time is to be properly set to about 1 to 5 seconds.
After applying a predetermined heat treatment to the granular material, the treated granular material is cooled. This cooling operation is applied for the reason of preventing the alpha starch layer being weakened due to the continuous heat application after the pasted starch is made into an alpha state and preventing the granular material from being changed in quality due to the temperature transmission to the inner portion of the granular material. The cooling operation is performed by changing the temperature to a temperature (about 40 to 50xc2x0 C. or less) at which the weakening and the change in quality are not generated before the weakening and the change in quality are generated (within about 1 to 10 seconds after the heating). The purpose can be achieved by bringing the alpha starch layer into contact with the air at a room temperature.